[Linuxptp-users] issues with mixed software timestamp / hardware timestamp setup

[Frank D. <fr...@ka...>]

Hello,

I'm running a mixed setup  of hardware timestamps (linuxptp 2.0) on an
ubuntu trusty setup and software timestaps (linuxptp 1.8 from debian
stretch on armhf, smsc95xx, same chip as raspberrypi) on an embedded system
based on debian stretch.

What i observe is:

   - the computers with hardware timestamps do sync fine
   - the embedded system claims to be in sync with the other computers (eg
   when i do pmc -u -b 0 'GET TIME_STATUS_NP'  the master_offset is less
   than 100usec on the embedded system and on the other computers too)
   - however, the clocks are totally not in sync (more than a minute apart
   as reported by "date")
   - phc2sys is running on the ubuntu trusty computers but not on the
   embedded system.

I have another test set where we replaced the trusty computers with ubuntu
bionic ones and run the latest git master, combined with the same embedded
system (debian stretch, linuxptp 1.8). On this setup, the sync works fine.

My question is: what could be the cause of a low master_offset but still no
clocks in sync ?
We will update all our systems to bionic soon, but i'd like to understand
the issue to know if it can occur in the future ...

Also, we have setup monitoring to send alerts when time is not in sync,
based on the output of "GET TIME_STATUS_NP". is this the right output to
monitor ?

Thanks!
Frank